An aerofoil structure typically comprises a torsion box structure, which includes one or more longitudinal spars, a plurality of transverse ribs, and is enclosed by structural covers. Aerofoil structures may be found in a variety of aircraft, spacecraft and wind turbine applications, for example.
When applied to aircraft wings and stabilizers the torsion box is often referred to as the “wing box”. A wing box construction used commonly in transport aircraft includes a front spar, a rear spar, an upper wing cover (skin) extending between the front spar and the rear spar, and a lower wing cover (skin) extending between the front spar and the rear spar. The front and rear spars may be formed as a C-section with upper and lower flanges extending from an upstanding web. The upper and lower wing covers may be attached to the flanges of the front and rear spars. Leading and trailing edge structures of the wing, such as the leading edge D-nose and leading/trailing edge access panels, may be supported by butt-straps attached to overhanging edges of the upper and lower covers.
The use of composite materials to replace traditional metallic aerospace materials provides opportunities to improve the wing box construction. In particular, it has recently been proposed to integrally form the front and rear spars with either the upper wing cover or the lower wing cover to form an Omega-shaped unitary component. Structural components, such as ribs, and aircraft systems can be installed within the Omega-shaped component before the other wing cover is attached to close the wing box. The Omega wing box is also known as a “U-box” when the lower cover is combined with the spars.
Combining the lower (or alternatively upper) wing cover with the spars eliminates the cover overhang traditionally used to support the leading/trailing edge structures.